High tension electric cable



April 28, 1936. w. A. DEL MAR 2,038,894

HIGH TENSION ELECTRIC CABLE Filed April 23, 1931 .15 WMM@ ZIM NVENTOR BY ATTORNEYS MMO Patented Apr. 28, 1936 uNiTED STATES PATENT OFFICE 2,038,894 HIGH TENSION ELECTRIC CABLE Application April 23, '1931, Serial No. 532,189

6 Claims.

This invention relates to electrical cables for high voltage service. Such cables may be either of the single conductor or multiple conductor type and more particularly such cables are of the type 5 provided with insulation which comprises impregnated fibrous material such as paper. In practice two kinds of impregnated paper. cables are in general use, viz. the liquid oil type and the viscous oil or solid type. impregnated paper l cables as heretofore made are structurally composed of copper, paper and lead with the parts within the cable so disposed that narrow helical and longitudinal passages occur throughout the cable. Such passages may be spaces between l surfaces of paper tapes, spaces between edges of the tapes, spaces between strands, hollow cores in conductors, or passages in iiller spaces. As enumerated the passages are set forth in the order of the ratio of their surfaces to their crosssectional areas, which order is also the order of their capillary attraction for the oil which they may contain when the cable is impregnated.V

It will be appreciated that the flow of oil in these passages depends not only upon the surfaceA tension characteristic of the passages in the structure but also upon the viscosity of oil which is used. Experience has demonstrated that the liquid oil type of cable has decided superiority over the solid type from the standpoint of dielectric strength and life under dielectric stress. On the other hand experience has also demonstrated that the liquid oil type is distinctly inferior to the solid type in regard to handling and maintenance in operation, due to the virtual impossibility of l maintaining permanently oil-tight a lead sheath possibly many miles long with numerous joints and connections in which large hydrostatic heads may occur.

The present invention has for its object'the f 40 provision of a cable which will have the superior dielectric strength of a liquid oil type of cable and which cable will at the same time possess the improved handling and maintenance properties of the solid type of cable.

l '45 A further object of the present invention resides in the provision of a cable which has a thin oil insulating medium in the insulation adjacent the conductor portion of the cable and which has a viscous oil impregnation in the insulation surrounding the portion of the cable insulation which contains the freely .owing liquid oil.

, A further object of the present invention resides in the provision of a cable nhaving liquid oil disposed in thel insulating material adjacent the .55 conductor and an outer insulated portion impregnated with viscous oil and with an oil impervious wall between the two portions of the cable.

Further and other objects of the present invention will be hereinafter set forth in the accompanying specification and claims and shown in 5 the drawing in which The iigure shows one and a preferred embodiment of my invention.

According to the present invention an improved cable having the superior dielectric characterl0 istics of an oil filled cable is provided by utilizing liquid oil for suppressing the initiation of failures in the most highly stressed parts of the dielectric. In other portions of the cable, especially in the v outer portions or layers of insulation which are l5 most exposed to oil leakage and where the dielectric stresses are not so great, viscous or solid impregnating compounds are employed so that ultimately the entire cable combines the dielectric excellence of an oil lled cable with the ease 20 of mechanical handling and the superior operating characteristics of a cable of the solid type.

According 4to the present invention and as shown in the drawing, I0 is a single conductor provided with paper or other fibrous wrappingsv 25 I l. This inner portion of the cable is irnpregnated and filled with thin oil having relatively low viscosity. The viscous or heavy oil impregnated portion of insulation preferably comprises paper or other iibrous wrappings i3 impregnated in the 30 usual way with viscous oil or grease. In practice and according to one embodiment of the invention the inner quarter of the insulation is impregnated with thin oil and the outer threequarters with viscous oil. However, such propor- 35l tions can bel widely varied as will occur to those skilled in the art.

Preferably to separate the thin oil impregnated section of th`e cable from the viscous oil impregnated section and to prevent the dissipation oi 40 the thin oil from theinner part to and/through the outer part of the cable, provision is made for providing, intermediate the two portions, an

voil impervious wall designated I2 on the drawing. In practice such wall I2 which is impervious 45 to oil may be o1' varnished cambric. While in the preferred construction such oil impervious wall is in the form of a. non-conducting envelope it will be appreciated that conducting materials might also be used for. this oil impervious wall 50 or envelope.

It will be understood that in lieu of using paperV wrappings I3 impregnated with viscous oil, other materials may be used for example, vare nished cambrlc or rubber` may be used. Prefer- Vclaims the term conductor is to be considered broadly as defining a structure wherein one or more conductors are employed.

In the making of cable with viscous oil in the external layers and a thin oil in the inner layers it is preferred practice to seal the ends of the cable, then laterally impregnate the outer layers with hot compound in a vacuum tank, and thereafter allow the cable to cool. The end seals are then removed and thin oil is drawn into one end of the cable and longitudinally therethrough by applying a vacuum to the opposite end of the cable. Alternatively the thin oil can be introduced by a lateral impregnation before the application of the layers I2 and I3.

While I have shown a single conductor, and explained that multiple conductors might be used in which case each conductor could be wrapped with a wrapping of paper or fibrous material pervious to oil. Such wrapping could be subdivided by an oil impervious layer substantially as hereinafter described so that the inner portion of. the cable adjacent the conductor could be impregnated with thin oil and so that viscous oil could be impregnated or introduced into the outer layers.

In lieu oi' utilizing varnished cambric as the oil impervious layer, wall, or partition I2, a thin lead sheath could be utilized or a cellophane layer or wrapping provided at this point. It is only necessary that such material should be impervious to oil so as to sub-divide the pervious wrappings by a wall which is substantially impervious to oil.

In its preferred embodiment, my improved cable comprises a conductor with wrappings or enveloping material thereon and which are of such nature as to be pervious to oil. Such wrapping or envelope is sub-divided by a partition wall, layer or envelope of oil impervious material so that thin oil may be disposed in the inner portion of the cable and prevented from permeating into the outer portion of 'the cable which is impregnated with heavy oil.

Certain subject matter of the instant application is being claimed in my copending application, Serial No. 29,784, filed July 5, 1935.

What I claim is:

1. An electrical cable comprising a conductor, an envelope of oil pervious insulating material,

a layer of substantially oil impervious material dividing said insulating material envelope into two layers, an impregnation of viscous oil on the less highly stressed side of the impervious layer and an impregnation of thin oil on the more highly stressed side of said layer for the purpose described.

2. A method of impregnating a paper insulated cable which consists in deilnitely separating the inner and outer paper insulating portions of the cable and thereafter impregnating the outer insulating part oi' the cable by a lateral impregnavtion with a relatively viscous oil and the inner insulating part of the cable by a longitudinal impregnation with a relatively thin oil which is capable of freely flowing endwise through the cable.

3. An electrical cable comprising the usual conductor and fibrous wrappings therefor and a viscous oil on the exterior convolutions of said wrappings and a thin oil impregnation in the interior portion of the cable and means for separating the thin oil impregnated part of the cable from the viscous oil impregnated part of the cable.

4. An electrical cable comprising a conductor,

pervious to oil, other :fibrous insulating material over said enveloping coating and thin oil impregnating material in the inner insulating portion of the cable in said first mentioned fibrous material. and viscous oil impregnating material upon the outer insulating portions of the cable in said second mentioned insulating material.

5. An electrical cable comprising a plurality of conductors, an envelope of oil pervious paper on each conductor, partitions of material substantially impervious to oil dividing the aforesaid oil pervious paper envelope into two layers, an impregnation of viscous oil or grease in the pervious paper on the less highly stressed side of the impervious partitions, and an impregnation of thin oil in the pervious paper on the other side Where the stress is greater.

6. An electric cable comprising a conductor, an envelope of oil pervious material such as paper, a partition comprised of a material which is substantially impervious to oil and which partition divides said envelope into two layers, and oily impregnating material in both of the aforesaid layers, said oily material at points Where dielectric stresses are highest being free flowing when the cable is in use, said oily material at points where dielectric stresses are relatively lowest being viscous and not free flowing when the cable is in use.

WILLIAM A. DEL MAR. 

